Concrete masonry is a popular construction material because its inherent attributes satisfy the diverse needs of both interior walls and exterior envelopes over a wide array of applications. While these attributes are the primary basis for concrete masonry’s popularity, performance should not be taken for granted. Cracks in building assemblies and building materials may result from restrained movement originating within the material, as with volume changes due to moisture loss or gain, or from temperature expansion or contraction. Cracking may also be caused by movements of adjacent or supporting elements or systems, such as deflection of beams or settlement of foundations. In many cases, movement is inevitable and must be accommodated or controlled, which requires an understanding of the sources of stress that cause cracking. While would be a simple matter to prevent cracking if there were only one cause or variable, in reality crack mitigation requires identifying and addressing a combination of potential sources.This Tech Note reviews the common causes of cracking, from both internal and external sources, in concrete masonry construction and presents proven strategies and detailing approaches to mitigate and control shrinkage-induced cracks. The Solutions Summary section of this Tech Note provides a summary overview of these recommendations, with more detailed explanation, construction details, and background provided in the subsequent discussion.
There are many types of construction joints each with different names incorporated into masonry construction for varying purposes. In the context of this Tech Note, the following joint terms and their associated meanings are used. Other regional terms or expressions may also be used to convey the same functional intent as those here.
- Control Joint – A joint used to break up a large field of concrete masonry into discrete panels for the purpose of allowing shrinkage and mitigating cracking.
- Isolation Joint – A joint used to separate one section of concrete masonry from another to prevent the transfer of loads or to accommodate differential movement within the system.
- Movement Joint – A generic term for a joint that may be intended to serve in multiple functions or accommodate multiple sources of movement.
- Relief Joint – A weakened section of reinforced concrete masonry used to control and isolate the formation of shrinkage related cracks.
- Expansion Joint – Used primarily with clay masonry construction to accommodate the expansion of the clay masonry units; typically not used with concrete masonry construction.
